After selecting New Patient from Plaque Simulator's File menu you will be prompted to create a folder for the new patient. In general, you should have already created a folder for the new patient and put all of the patient's image files into it, so most of the time you will respond No to this prompt.

If you responded Yes to the offer to create a folder you will be prompted for the name of the new patient.

The OSX file navigation dialog will open. Navigate so as to create the new folder in your Plaque Simulator Patients folder. Click the New Folder button.

Name the new folder and click the Create button.